...or anyone else would like to venture an opinion.

With all other factors being equal and assuming the ambient temperature is 80 degrees, does it take the same amount of energy to raise room temperature from 70 degrees to 90 degrees as it would to lower it from 90 degrees to 70?

Also, is the amount of energy necessary to raise it from 70 to 80 or lower it from 90 to 80 the same as to raise it from 80 to 90 or lower it from 80 to 70?

And lastly, would the energy need be different if the ambient temp in the above exercise was lower or higher i.e. 50 degrees and going up to 60 or down to 40 or 100 degrees and going up to 110 or down to 90?
TIA...

I'll leave this to him, if he wants to tackle it. It made my head hurt just reading the question!

No.

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In reviewing your response Case, the word "succinct" comes to mind. Does your answer refer to the first, second, third or all three of my questions?

No to all of them mate, they will all require different amounts of energy to achieve, especially since A/C systems have different levels of efficiency for heating and cooling.

Ontop of that, the insulating properties of the room make a difference to how effectively it can be heated or cooled.

Im not sure what sort of room A/C youre talking about. Comercial or domestic? This will make a very big difference to the outcome, and will also need the info on where the ambient air temp is taken, whether it was outside or in the airconditioned room.

If we are talking comercial A/C, the outside temp will play a big role in the amount of energy required to do what youre after. If its hot outside, and youre trying to raise the temp inside, you would draw in makeup air from outside, hence potentially making the unit more efficient. If its hot outside and youre trying to cool a room, you would have the system using a mix of return air and makeup air in order to recycle some of the conditioned air. If its cold ouside, you would be using return air, with the electric duct heater coils going at varied rates depending on the room temp, the desired temp, and the temp of the dehumidified air from the evaporator.

If youre talking about domestic A/C, they generally dont have a makeup air intake, so the only air you have to work with is the air allready in the room.

Thanks, Case. I had no particular application in mind, I was just trying to figure out if it's cheaper to heat or cool and whether the cost increases arithmetically or exponentially as you move away from a base point (kind of like a tractor pull). It looks like there are too many variables to even generalize...

Not sure if this applies directly John, but check out this link

http://autorepair.about.com/od/autorepair12/l/aa061904a.htm

pay particular attention to page 5, if I understand it correctly heating or cooling requires the exact same amount of energy. If I don't understand it correctly it wouldn't be the first time, and probably won't be the last.

Yes mate, no 2 aplications will be the same, and no 2 conditions will be the same either. Air conditioning can be quite a complex issue.

When you say HVAC and talk about heating and cooling a room, that leads me to the bit about the comercial A/C systems, which are simular to vehicular HVAC in that the evaporator is only able to cool and dehumidify, and heating is then done by electric resistance duct heaters, which are like the heater core in a car.

Domestic reverse cycle works differently.

Here is a couple links, i couldnt find one about the workings of a reverse cycle system.

http://en.wikipedia.org/wiki/HVAC#Heating_energy
http://en.wikipedia.org/wiki/Air_conditioning

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That is related to vehicular HVAC, where the heater core is full of hot coolant.

So did CC ever have anything to say about this? I guess the other CC, Case, took care of it.

I had a crack at it yeah, im not an A/C expert, but i have a fair bit to do with it at work.

After abit of reading late last night i notice that you also have simular ducted domestic systems over there as comercial systems, most ducted systems here are reverse cycle.

Sorry, been gone a few days, trying to catch up on everything is getting harder and harder as this place grows!

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Yes, all things being equal. Although in reality heating and cooling use different forms of fuel and work at different efficiencies, and cost different rates.

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If it's perfectly insulated, then yes. But if its perfectly insulated, ambient outdoor temp doesn't matter anyways. If it's 80F outside, and you have a poorly insulated building, or windows open, you can cool it from 90 to 80F for free, whereas going from 80F to 90F would cost some energy.

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Nope, same thing.

To summarize, you're correct to focus on temperature difference driving heat transfer, but there's also way more to it than that. Most buildings, in the southwest at least, where the cold and hot seasons can be about the same temp difference from indoors, have more air conditioning than heating ability.

This is because the buildings are constantly being heated from things that have nothing to do with temperature difference, such as solar loads (radiation) from the sun, thermal mass storage (concrete walls feeling cool in the day, and warm at night), internal heat loads (people, appliances), and then you've got air infiltration or ventilation, where you're getting some outdoor air entering the room directly. This can add or remove heat.

The other trick, is it's easy to heat because a typical gas fired heat exchanger can put out really toasty air. A refrigerant cooling coil though, can only go so cold before it freezes the moisture in the air. So for the same amount of heating/cooling, you need more air through the cooling coil because the coil may be only 30F colder than room temp, while the gas heat exchanger in your furnace can be really fucking hot.

Now this is only talking about sensible heat transfer. In commercial buildings, and residential in some climates, you have to consider latent heat, which is basically the amount of moisture/humidity in the air. If I'm in Florida, and it's 75% humidity in the morning, I can't just bring cool ventilation air in to my building to keep the workers happy. I'd have to run my air conditioner to condense moisture out of the air, and then maybe even reheat it to get it back to a comfortable temp. Sort of like how the defroster works on your car. Removing moisture costs a ton of energy. A 4-ton air conditioner might only actually do 2.5 tons of sensible cooling in a really humid area. That's when the owner sues the contractor and hire us to redesign it.

Thanks very much for taking the time to explain all of that...